HOW TO DO THREE-DIMENSIONAL MAPS:

Three dimensional photos and maps can help resource managers quickly analyze hydrologic, aesthetic, habitat type, fire suppression and other site management factors. Once mastered, the steps in creating 3D land images are fairly simple.

Computer-based representations of areal geology extended into the subsurface as 3-dimensional geologic maps can now be developed to provide continuous quantitative 3-D geologic information for a variety of practical needs. Such 3D databases and appropriate computer software will allow even the inexperienced user to figuratively "walk around" in the earth to examine the data and extract needed information. One important application unique to 3D geologic maps is predictive process modeling of geologic, tectonic, and hydrologic processes needed for land-use planning, hazard mitigation, and resource management. Examples of immediate applications of 3D maps include ground shaking estimation, refined earthquake relocation, fault segmentation analysis for probabilistic earthquake forecasting, resource exploration, contaminant source and dispersion pathway definition, and ground water flow modeling for resource management.

Traditional geologic maps, which show the distribution and orientation of geologic materials and structures at the ground surface, have served for many decades as effective tools for storing and transmitting geologic information. The introduction enhanced traditional geologic maps in terms of ease of use and communication of surface geologic information. However, these maps, even enhanced with capabilities, are insufficient for storing and transmitting subsurface information, information that is critical in the role of the map as a window into the subsurface. Fortunately, advances in computer hardware and geologic modeling and visualization software now provide us with the potential to construct 3D geologic maps that retain all the information in a traditional geologic map while quantitatively extending this information into the subsurface.

The goal of the project is to produce, display, and release quantitative 3-dimensional geologic maps.The 3D maps will include, in a continuous quantitative volumetric format, the information contained in traditional 2D geologic maps and thus can form the bases for predictive process modeling as well as address, in 3-dimensions, traditional geologic map-based questions. A critical component of these 3D maps will be the inclusion of a continuous representation of uncertainties, a feature only partly realized in traditional geologic maps. Fundamental techniques peculiar to 3D map generation will be developed to accomplish this goal.

We follow a rigorous sequence of procedures in constructing our 3D geologic maps. First, point data representing discrete 3D locations on a given geologic surface (e.g. a fault) are assembled from surface geologic mapping, well data, geophysical inversions, seismicity, geologic reasoning, and any other sources available. A numerically defined surface is then passed through these data points in order to predict the position of the geologic surface throughout the 3D map volume. Uncertainty as a function of position is assigned to each surface. Once all important surfaces have been defined in this way, they are assembled into a 3D structure according to "rules" that specify how the surfaces interact (i.e., which surfaces truncate which). The surfaces, together with the interaction rules, define volumes that correspond to fault blocks and geologic units. Properties are then assigned throughout the 3D geologic map according to xyz location, geologic identity, proximity to surfaces, geologic process model considerations, or some combination of these parameters. Thus the 3D geologic map exists in the computer as a collection of numerically defined surfaces with associated uncertainties, a set of rules that specify spatial interactions where surfaces encounter each other, and a volume distribution of properties with associated uncertainties. Note that because the map is numerical, it is capable of an enormous dynamic range when defining features. Theoretically, strata a few cm thick could be faithfully included in a geologic map that extends through the entire earth's crust.

Once the 3D map has been assembled within the computer, graphical representations permit the user to examine the map from various directions, slice it to examine its interior, disassemble it to examine individual geologic units, compare it graphically with other geographically defined data, and perform a number of other tasks. While graphical representations are valuable tools with which to make use of the 3D geologic map they are simply graphical extracts from the real 3D geologic map that exists digitally within the computer.